What do you think.

Ok I need some input maybe. So my fiancé is pregnant no big suprise there as we have been trying for 6 months now. I just recently found out that it could possiblynot be mine. She had a one night stand with a guy March 3rd. The obgyn said that he could eatimate the date it was concived and he said march 12th give or take a few days. She has a hard time getting pregnant due to ovarian cancer and had one ovary already removed since we were together. Now the other guy said he would just rather see her have an abortion and be done with it so he can move on with his life. I don't want to do that for the fact there is a 50% chance that it could be mine. She has offered to give a dna rest once the baby is born to determine who's exactly it is. My question is should we get the dna test done. My concern is that if I stay with her and work through this that I will be to attached to the baby and it would crush me to know if it wasn't mine. This is the first time that she has ever cheated on me but I don't know if it was really cheating as we broke up for a few days when this happened. Someone please give me some input as I'm confused. We are currently talking and working on things but this is where I'm hitting the road block. Dna test or not amd just call it mine and raise it like it's nome amd not know the difference.